TiN has been widely used as hard layer on cutting tools, but the poor oxidation resistance at temperatures above 500° C. has created an interest in ternary or quaternary compounds, e.g. Ti—Al—N and Ti—Cr—Al—N. More complex quaternaries, e.g. Ti—Al—Si—N, have been reported and described as super hard H>45 GPa due to a two phase structure consisting of crystalline phase of NaCl-type in combination with amorphous Si3N4 or SiNx. These coating materials show an improved oxidation resistance and improved performance in machining of hardened steels.
EP 1736565, WO 2006/118513, and EP 0588350 disclose hard coatings comprising (Ti,Si)N layers.
U.S. Pat. No. 7,083,868 and U.S. Pat. No. 7,056,602 disclose hard coatings comprising (Ti,Al)N layers.
Coating optimization has also been obtained by applying different concepts of multilayer as: alternating Ti and Al containing layers (U.S. Pat. No. 6,309,738), oxygen and non-oxygen containing layers (U.S. Pat. No. 6,254,984), one of the layers stacked in the multilayer consists itself of a multilayer (U.S. Pat. No. 6,077,596), alternating nitrogen content (U.S. Pat. No. 5,330,853) or using one metastable compound (U.S. Pat. No. 5,503,912) or as aperiodic multilayer (U.S. Pat. No. 6,103,357).
The trends towards dry-work processes for environmental protection, i.e., metal cutting operation without using cutting fluids (lubricants) and accelerated machining speed with improved process, put even higher demands on the characteristics of the tool materials due to an increased tool cutting-edge temperature. In particular, coating stability at high temperatures, e.g. oxidation- and wear-resistance, have become even more crucial.
Surprisingly, it has been found that a coating comprising alternating cubic structured MeN, (Ti,Al)N and (Ti,Si)N layers leads to improved wear and temperature resistance.
What is needed is a coated cutting tool with improved high temperature performance during metal cutting. The invention is directed to these, as well as other, important needs.